The project will study the secretion and action of the antidiuretic hormone, arginine vasopressin, in patients with insulin dependent diabetes mellitus. The osmotic and hemodynamic control of vasopressin secretion will be assessed independently as will the effects of exogenous vasopressin on urinary concentration, arterial pressure, intestinal motility and glucose homeostasis. Salt and water balance, peripheral nerve conduction, autonomic nerve function, plasma norepinepherine, renin activity, glucagon and Hgb Al also will be measured to determine if hypovolemia, neuropathy, hyporeninemia, hyperglucagonemia, or poor metabolic control are related in any way to the observed abnormalities in vasopressin secretion of action. All studies will be performed under BiostatorR control of blood negar to assess the interaction between insulin delivery and vasopressin dysfunction. The results may explain certain disturbances of water balance, blood pressure control or glucose homeostasis in diabetics and suggest new and better ways of managing these complications.